Conductive adhesive and connection structure using the same

ABSTRACT

A mounting technique with improved adhesive strength and higher reliability against bending stress is provided with the use of a conductive adhesive including a binder resin and a metal filler as main components, in which a functional group is introduced into the molecular chain of the binder resin to form a multidentate bonding with an electrode metal easily. As a thermoplastic resin, at least two kinds of functional groups selected from the group consisting of a carbonyl group, a carboxyl group, an amino group, an imino group, an iminoacetic acid group, an iminopropionic acid group, a hydroxyl group, a thiol group, a pyridinium group, an imido group, an azo group, a nitrilo group, an ammonium group and an imidazole group are introduced. Accordingly, a strong bond with the electrode metal can be achieved. The conductive adhesive is screen-printed to an electrode disposed on a substrate, and after an electrode of a component is mounted, the structure is heated so as to create a mounted structure.

This application is a divisional of Ser. No. 09/751,621 Dec. 29, 2000,now U.S. Pat. No. 6,521,144.

FIELD OF THE INVENTION

The present invention relates to a conductive adhesive used forsolder-free mounting of electronic components and a structure connectedby using the same.

BACKGROUND OF THE INVENTION

In recent years, due to the increased environmental consciousness, theelectrical industry now faces the movement to abolish totallylead-containing solder used for mounting of electronic components, andthis movement is becoming significant.

As for lead-free mounting techniques, mounting techniques usinglead-free solder have been developed keenly and a part of thedevelopment has come into practical use. However, still a number ofproblems remains to be solved, such as influence of a high mountingtemperature on low heat-resistant components or lead-free electrodes.

On the other hand, only a few examples of lead-free mounting with theuse of a conductive adhesive has been reported so far, which has thefollowing advantages besides the aspect of lead-free mounting.

First, the processing temperature of around 150° C. is lower than thetemperature for soldering, and electronic components with higherperformance can be realized with low cost. Secondly, the specificgravity of a conductive adhesive is about half that of solder, so thatelectronic equipment can be lightened more easily. Thirdly, since theconnection is not achieved by means of metal as in soldering, metalfatigue does not occur, and the reliability of mounting is excellent.

Therefore, it is expected that a revolutionary mounting process thatfulfills the needs of environment, low cost, and high reliability can berealized by completing the mounting technique using a conductiveadhesive.

The problem with the use of a conductive adhesive for mounting is thatthe adhesive strength is lower than that of solder. In particular, thestrength against bending stress is about {fraction (1/10)} of that ofsolder, so that an electronic component with a large area to whichbending stress easily is applied sometimes suffers from the separationof the electrode with the conductive adhesive at the interface, therebycausing connection failures.

Numerous attempts to improve the adhesive strength have been reported,but not even one technique is capable of achieving the same strength asthat of solder. One representative example will be shown below.

As described in the publication supervised by Hiroo Miyairi,“Development of Functional Adhesives and the New Technology” (edited byCMC, Jun. 30, 1997, 194 pages), for example, a number of techniques toimprove the adhesive strength by adding an organic metal called a silanecoupling agent into the adhesive material, which can form a chemicalbond with both resin and metal, has been reported.

However, the aforementioned techniques utilize either a dehydrationreaction or a substitution reaction, so that the reactivity of thecoupling agent with resin or with metal was poor, and the conditions(temperature, concentration of hydrogen ion, etc.) for optimizing thereaction could not be determined clearly, and so forth. Therefore, aconsiderable improvement of the adhesive strength was difficult to beachieved.

Furthermore, JP9(1997)-176285A proposes the use of a resin with aphosphoric ester group introduced into the skeleton as a binder resin.According to this method, the functional group in the binder resin isadsorbed to the metal, so that some improvement of the adhesive strengthcan be achieved. However, the adsorptive power is poor in comparisonwith a covalent bond or a coordinate bond, so that considerably improvedeffects could not be obtained.

As described above, the improvement of the adhesive strength has beenthe key factor to make the practical use of the mounting technique usinga conductive adhesive.

SUMMARY OF THE INVENTION

It is an object of the present invention to solve the conventionalproblems described above by providing a conductive adhesive havingconsiderably improved adhesive strength and higher reliability againstbending stress. Another object of the present invention is to provide astructure connected by using this conductive adhesive.

To achieve the above object, a conductive adhesive of the presentinvention includes a binder resin and a metal filler as main components,wherein the binder resin contains a functional group in its molecularchain that forms a multidentate bonding with an electrode metal afterthe binder resin is adhered.

A connection structure of the present invention is formed by using aconductive adhesive to connect the adhesive with an electrodeelectrically, wherein the conductive adhesive includes a binder resinand a metal filler as main components, and the binder resin contains afunctional group in its molecular chain that forms a multidentatebonding with an electrode metal after the binder resin is adhered.

In the present invention, the multidentate bonding refers to a state inwhich multidentate ligands (a plurality of chelating ligands) introducedinto the binder resin form coordinate bonds with the electrode metal. Inother words, the adhesion is not achieved only by using the ordinaryweak van der Waal's power by hydrogen bonding, but instead, a chemicalbond (coordinate bond) is formed between the binder resin and theelectrode.

The method of introducing a multidentate ligand into a binder resin willbe explained by way of the following embodiments.

Embodiment 1

In the first method, a resin into which a desired multidentate ligandwas introduced was used as an additive component in the binder resin (areactive thinner, a hardener, or the like).

For example, a linear epoxy resin with a molecular chain into which adicarbonyl group expressed by the chemical formula 1 below wasintroduced is mixed with a ring-opening catalyst, which then is appliedto the surface of an electrode (Cu foil). When the resin is heated andhardened, the dicarbonyl group in the central part of the molecule formsa coordinate bond with the electrode (Cu foil) expressed by the chemicalformula 2 below. Naturally, the epoxy rings at the both ends of themolecule open and form bridge bonds.

The binder resin used here includes as the main component an ordinaryepoxy resin without any ligand (bisphenol A, bisphenol F, a novolakepoxy resin). The above resin into which the multidentate ligand wasintroduced is used by mixing and kneading so as to be contained in thebinder resin in an amount between 10 and 50 wt %.

Furthermore, a ligand can be introduced into a resin to be used as ahardener in the binder resin, not only for the reactive thinner.

Embodiment 2

In the second method, a resin into which a desired multidentate ligandwas introduced was used as the main component (the component containedin the largest amount) in the binder resin.

For example, a bisphenol F-type epoxy resin with a molecular chain intowhich a dicarbonyl group expressed by the chemical formula 3 below wasintroduced is mixed with a ring-opening catalyst, which then is appliedto the surface of an electrode (Cu foil). When the resin is heated andhardened, the dicarbonyl group in the central part of the molecule formsa coordinate bond with the electrode (Cu foil) as in Embodiment 1.

The binder resin used here includes as the accessory component anordinary epoxy resin without any ligand (a reactive thinner, a hardener,or the like). The above resin into which the multidentate ligand wasintroduced is used by mixing and kneading so as to be contained in thebinder resin in an amount between 30 and 100 wt %.

In the adhesive and the connection structure of the present inventiondescribed above, it is preferable that the multidentate bonding isformed in a number between 2 and 4. Naturally, the number of themultidentate bonding may be larger.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that the resin containing a functional group inits molecular chain that forms a multidentate bonding is present in anamount between 10 and 100 wt % of the total resin.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that, taking the conductive adhesive as 100 wt%, the binder resin is contained in an amount between 6 and 25 wt %, andthe metal filler is contained in an amount between 75 and 95 wt %.Besides, if necessary, a hardener, a hardening catalyst, a crosslinkingagent, and a ring-opening catalyst for the binder resin, a dispersingagent for the metal filler, a viscosity modifier, a pH modifier, or thelike may be added optionally. Therefore, in the present invention, “maincomponents” in the “including a binder resin and a metal filler as maincomponents” refers to the constitution in which the binder resin and themetal filler together comprise at least 90 wt % of the conductiveadhesive.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that at least two functional groups are present,which may be the same or different, selected from the group consistingof a carbonyl group, a carboxyl group, an amino group, an imino group,an iminoacetic acid group, an iminopropionic acid group, a hydroxylgroup, a thiol group, a pyridinium group, an imido group, an azo group,a nitrilo group, an ammonium group and an imidazole group.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that the metal filler is at least one particleselected from the group consisting of silver, silver-plated nickel andsilver-plated copper. When the surface of the metal filler is silver, itdoes not react with the ligand of the binder resin but the ligand reactsselectively with the electrode metal. However, when the ligand of thebinder resin is contained in a large amount, even if copper is used asthe metal filler, for example, since not all the ligands react with themetal filler, copper also can be used as the metal filler.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that the binder resin is at least one resinselected from a thermoplastic resin and a thermosetting resin.

Furthermore, in the adhesive and the connection structure describedabove, it is preferable that the thermoplastic resin is at least oneresin selected from the group consisting of a polyester resin, asilicone resin, a vinyl resin, a vinyl chloride resin, an acrylic resin,a polystyrene resin, an ionomer resin, a polymethylpentene resin, apolyimide resin, a polycarbonate resin, a fluororesin and athermoplastic epoxy resin.

According to the invention described above, the mounting technique bythe conductive adhesive with considerably improved adhesive strength canbe realized.

When the conductive adhesive of the present invention and the electrodemetal contact each other, the ligand of the binder resin very easilyreacts with the metal, so that the ligand is coordinated quickly withthe electrode metal to form a chelating ligand, i.e. a strong chemicalbonding. Since the ligand is bonded to the molecular chain of the resin,the bonding also is strengthened between the binder resin and theelectrode metal as well as between the conductive adhesive and theelectrode metal.

The connection structure of the present invention is formed byelectrically connecting the conductive adhesive of the present inventionwith the electrode, so that this connection structure has improvedadhesive strength than conventional connection structures. Moreover,since the thermoplastic resin has excellent flexibility in comparisonwith a thermosetting resin, this conductive adhesive can achieve abonding with excellent stress relaxation capability against bendingstress.

The connection structure of the present invention preferably is formedby mounting a component and a substrate by using the conductive adhesivedescribed above, which can improve the adhesive strength against bendingstress even more.

The present invention can be used in place of the conventional solder,for example, as a conductive adhesive to bond a semiconductor substratewith an electronic component chip. Furthermore, the conductive adhesivealso can be applied to a conductive paste by filling the conductiveadhesive into through holes made in an electrical insulating basematerial so as to achieve electrical continuity in the thicknessdirection of the electrical insulating base material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view showing a mounted structure used forthe evaluation of one embodiment of the present invention.

FIG. 2 is a cross-sectional illustrative view showing the evaluationmethod of one embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

Hereinafter, the present invention will be described by way of exampleswith reference to drawings.

Common Experimental Method

FIG. 1 is a side view of a mounted structure used for the evaluation. Aconductive adhesive 3 is screen-printed onto an electrode 2 disposed ona substrate 1, and after an electrode 5 of a component 4 is mounted, thestructure is heated in an oven at 150° C. for 30 minutes. Thus, themounted structure was created. The material used for the substrate 1 andthe component 4 was the same, and the material used for the electrode 2and the electrode 5 was the same.

The evaluation method is shown in FIG. 2. First, pressure was providedto the component 4 from the rear side of the mounted structure createdas above by using a substrate pushing jig 6. The amount of deflectionwas measured when the connection resistance had risen to at least twiceas much as the initial value. Then, the adhesive strength against thebending stress was evaluated. The distance between substrate fixing jigs7 and 8 was determined to be 100 mm.

The substrate and the component will be described more in detail.

(1) Component: 0 ohmic resistance base material; alumina or a glassepoxy substrate (3216 size) electrode specification; as shown in Table 1

(2) Substrate base material; alumina or a glass epoxy substrate(30×150×1.6 mm) electrode specification; as shown in Table 1

(3) Conductive adhesive filler; silver powder (85 wt %) (averageparticle diameter: 3 to 10 μm) binder resin (15 wt %); as shown in Table1

Hereinafter, the respective embodiments will be explained in detail. InExamples 1 and 2, the conductive adhesive includes a material in which afunctional group was introduced into a thermosetting resin. In Examples3 and 4, the conductive adhesive includes a material in which afunctional group was introduced into a thermoplastic resin.

EXAMPLE 1

Example 1 is an example, as already explained in Embodiment 1, in whicha resin into which a multidentate ligand was introduced was used as anadditive component (a reactive thinner).

The binder resin used for the conductive adhesive was obtained by mixing15 wt % of a reactive thinner in which a dicarbonyl group expressed bythe chemical formula 4 below was introduced into its molecular chain, 75wt % of a bisphenol F epoxy resin, 5 wt % of a hardener (maleicanhydride), and 5 wt % of a solvent (butyl carbitol acetate).

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 2

The binder resin used for the conductive adhesive was the same epoxyresin as in Example 1 in which a dicarbonyl group was bonded to its sidechain (chemical formula 4 above). A conventional Cu thick foil was usedas the electrode.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 3

Except that a thermoplastic silicone resin was used in which adicarbonyl group was introduced into the side chain of siliconeexpressed by the chemical formula 5 below, the constitutions were thesame as in Example 1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 4

The binder resin used for the conductive adhesive was the resin in whicha dicarbonyl group was bonded to the side chain of a silicone resinexpressed by the chemical formula 4 above. A conventional Cu foil wasused as the electrode.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved. Furthermore, the adhesive strength was higherthan in Example 2.

EXAMPLE 5

Except that an epoxy resin was used in which the ligand to be introducedinto the resin was changed to an aminocarbonyl group in Example 1expressed by the chemical formula 6 below, the constitutions were thesame as in Example 1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 6

Except that the electrode was changed to a calcined Cu thick foil, theconstitutions were the same as in Example 5.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 7

Except that an epoxy resin was used in which the ligand to be introducedinto the resin was changed to a dicarbonyl group in Example 1 expressedby the chemical formula 7 below, the constitutions were the same as inExample 1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 8

Except that the electrode was changed to a calcined Cu thick foil, theconstitutions were the same as in Example 7.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 9

Except that an epoxy resin was used in which the ligand to be introducedinto the resin was changed to a dicarbonyl group expressed by thechemical formula 8 below, the constitutions were the same as in Example1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 10

Except that the electrode was changed to a calcined Cu thick foil, theconstitutions were the same as in Example 9.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 11

Except that an epoxy resin was used in which the ligand to be introducedinto the resin was changed to a dicarbonyl group expressed by thechemical formula 9 below, the constitutions were the same as in Example1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 12

Except that the electrode was changed to a calcined Cu thick foil, theconstitutions were the same as in Example 11.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 13

Except that an epoxy resin was used in which the ligand to be introducedinto the resin was changed to a dicarbonyl group expressed by thechemical formula 10 below (where n indicates a degree of polymerizationof about 2 in average), the constitutions were the same as in Example 1.

As a result, in comparison with the cases of Comparative Example 1 (aconventional conductive adhesive), Comparative Example 5 (a silanecoupling agent was added), and Comparative Example 7 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

EXAMPLE 14

Except that the electrode was changed to a calcined Cu thick foil, theconstitutions were the same as in Example 13.

As a result, in comparison with the cases of Comparative Example 2 (aconventional conductive adhesive), Comparative Example 6 (a silanecoupling agent was added), and Comparative Example 8 (an epoxy resininto which a phosphoric ester group was introduced), the amount ofdeflection at the time of NG rose, and the adhesive strength against thebending stress improved.

COMPARATIVE EXAMPLE 1

Except that a conventional conductive adhesive of the followingcomposition was used in place of the binder resin in Example 1, theexperiment was performed in the same manner as in Example 1.

bisphenol F-type epoxy resin 90 wt %

hardener (diethylenetriamine) 5 wt %

solvent (butyl carbitol acetate) 5 wt %

COMPARATIVE EXAMPLE 2

Except that a calcined Cu thick foil was used in place of the Cu foil inComparative Example 1, the experiment was performed in the same manneras in Comparative Example 1.

COMPARATIVE EXAMPLE 3

Except that a both-end hydrogen-dimethyl disilicone resin was used inplace of the binder resin in Example 3, the experiment was performed inthe same manner as in Example 1.

COMPARATIVE EXAMPLE 4

Except that a calcined Cu thick foil was used in place of the Cu foil inComparative Example 3, the experiment was performed in the same manneras in Comparative Example 3.

COMPARATIVE EXAMPLE 5

Except that a silane coupling agent was used in place of the binderresin in Example 1, the experiment was performed in the same manner asin Example 1.

COMPARATIVE EXAMPLE 6

Except that a calcined Cu thick foil was used in place of the Cu foil inComparative Example 5, the experiment was performed in the same manneras in Comparative Example 5.

COMPARATIVE EXAMPLE 7

Except that an epoxy resin in which a phosphoric ester group wasintroduced into its molecular skeleton was used in place of the binderresin in Example 1, the experiment was performed in the same manner asin Example 1.

COMPARATIVE EXAMPLE 8

Except that a calcined Cu thick foil was used in place of the Cu foil inComparative Example 7, the experiment was performed in the same manneras in Comparative Example 7.

All the results of Examples 1 to 14 and Comparative Examples 1 to 8above of the present invention are shown in Table 1 below.

TABLE 1-1 Conductive Adhesive Binder Resin Rate of Content ExperimentalResin introduced with ligand (in total resin) Conductive No. SkeletonLigand (wt %) particle Example 1 epoxy dicarbonyl group 15 Ag Example 2epoxy dicarbonyl group 15 Ag Example 3 silicone dicarbonyl group 15 AgExample 4 silicone dicarbonyl group 15 Ag Example 5 epoxy aminocarbonylgroup 15 Ag Example 6 epoxy aminocarbonyl group 15 Ag Example 7 epoxydicarbonyl group 15 Ag Example 8 epoxy dicarbonyl group 15 Ag Example 9epoxy dicarbonyl group 15 Ag Example 10 epoxy dicarbonyl group 15 AgExample 11 epoxy dicarbonyl group 65 Ag Example 12 epoxy dicarbonylgroup 65 Ag Example 13 epoxy dicarbonyl group 65 Ag Example 14 epoxydicarbonyl group 65 Ag Compar. epoxy none 0 Ag Example 1 Compar. epoxynone 0 Ag Example 2 Compar. silicone none 0 Ag Example 3 Compar.silicone none 0 Ag Example 4 Compar. epoxy none (silane 0 Ag Example 5coupling agent added) Compar. epoxy none (silane 0 Ag Example 6 couplingagent added) Compar. epoxy a phosphoric ester 15 Ag Example 7 groupCompar. epoxy a phosphoric ester group 15 Ag Example 8

TABLE 1-2 Substrate and Component Results of Bending Test ElectrodeSpecification Deflection at Initial Experimental Base Porosity Roughnessthe time of Resistance No. Material Material (vol%) (μm) NG (mm) (Ω)Example 1 glass epoxy Cu foil — 0.1 7.5 0.15 Example 2 alumina calcined2.0 — 9.6 0.20 Cu thick foil Example 3 glass epoxy Cu foil — 0.1 8.90.20 Example 4 alumina calcined 2.0 — 10.7 0.20 Cu thick foil Example 5glass epoxy Cu foil — 0.1 7.3 0.15 Example 6 alumina calcined 2.0 — 9.90.18 Cu thick foil Example 7 glass epoxy Cu foil — 0.1 7.4 0.16 Example8 alumina calcined 2.0 — 9.8 0.15 Cu thick foil Example 9 glass epoxy Cufoil — 0.1 7.6 0.12 Example alumina calcined 2.0 — 9.9 0.15 10 Cu thickfoil Example glass epoxy Cu foil — 0.1 7.7 0.22 11 Example aluminacalcined 2.0 — 10.0 0.20 12 Cu thick foil Example glass epoxy Cu foil —0.1 7.8 0.21 13 Example alumina calcined 2.0 — 10.1 0.19 14 Cu thickfoil Compar. glass epoxy Cu foil — 0.1 2.4 0.20 Example 1 Compar.alumina calcined 2.0 — 2.8 0.20 Example 2 Cu thick foil Compar. glassepoxy Cu foil — 0.1 0.7 0.20 Example 3 Compar. alumina calcined 2.0 —0.9 0.20 Example 4 Cu thick foil Compar. glass epoxy Cu foil — 0.1 3.20.10 Example 5 Compar. alumina calcined 2.0 — 3.3 0.20 Example 6 Cuthick foil Compar. glass epoxy Cu foil — 0.1 3.8 0.20 Example 7 Compar.alumina calcined 2.0 — 4.2 0.20 Example 8 Cu thick foil

In the Examples of the present invention above, the binder resins usedfor the conductive adhesive were only an epoxy resin and a siliconeresin, but other resins described in the Embodiments also are effectivefor use. Moreover, only a dicarbonyl group was shown as the ligandbonded to the side chain of the binder resin, but other ligandsdescribed in the Embodiments also may be used. Furthermore, only copperwas used as the electrode metal, but other metals generally used forelectrodes as described in the Embodiments also may be used.

According to the present invention, the problems with regard to themounting of conductive adhesives, i.e. the adhesive strength andparticularly the strength against the bending stress, can be solvedeasily. The present invention greatly contributes to the commercialapplication of the mounting technique using conductive adhesives.

The invention may be embodied in other forms without departing from thespirit or essential characteristics thereof. The embodiments disclosedin this application are to be considered in all respects as illustrativeand not limiting. The scope of the invention is indicated by theappended claims rather than by the foregoing description, and allchanges which come within the meaning and range of equivalency of theclaims are intended to be embraced therein.

What is claimed is:
 1. A conductive adhesive comprising a binder resinand a metal filler as main components, wherein the binder resin containsa functional group in its molecular chain that forms a multidentatebonding with an electrode metal after the binder resin is adhered,wherein taking the conductive adhesive as 100 wt %, the binder resin iscontained in an amount between 5 and 25 wt %, and the metal filler iscontained in an amount between 75 and 95 wt %.
 2. The conductiveadhesive according to claim 1, wherein the multidentate bonding isformed in a number between 2 and 4 per molecule.
 3. The conductiveadhesive according to claim 1, wherein the resin containing a functionalgroup in its molecular chain that forms a multidentate bonding ispresent in an amount between 10 and 100 wt % of the total resin.
 4. Theconductive adhesive according to claim 1, wherein at least twofunctional groups are present, which may be the same or different,selected from the group consisting of a carbonyl groups a carboxylgroup, an amino group, an imino group, an iminoacetic acid group, animinopropionic acid group, a hydroxyl group, a thiol group, a pyridiniumgroup, an imido group, an azo group, a nitrilo group, an ammonium groupand an imidazole group.
 5. The conductive adhesive according to claim 1,wherein the metal filler is at least one particle selected from thegroup consisting of silver, silver-plated nickel and silver-platedcopper.
 6. The conductive adhesive according to claim 1, wherein thebinder resin is at least one resin selected from a thermoplastic resinand a thermosetting resin.
 7. The conductive adhesive according to claim6, wherein the thermoplastic resin is at least one resin selected fromthe group consisting of a polyester resin, a silicone resin, a vinylresin, a vinyl chloride resin, an acrylic resin, a polystyrene resin, anionomer resin, a polymethylpentene resin, a polyimide resin, apolycarbonate resin, a fluororesin and a thermoplastic epoxy resin.